1. Field of the Invention
The present invention relates to an undercut self-cutting dowel including a body having a through-bore, load application means provided in a rear portion of the body, and a plurality of expansion tabs separated by axial slots and formed in a front, in the setting direction, portion of the body, and further including an expansion member held in the through-bore, projecting beyond a front end of the body, and widening in the setting direction, with the expansion tabs expanding upon displacement of the body over the expansion member.
2. Description of the Prior Art
As attachment systems in which small distances between axes and edges should be retained, generally, fastening systems with formlocking anchoring of the fastening elements are used. In addition to a possibility to anchor a head bolt in a construction component by pouring, such distance-critical attachments can also be formed by using attachment systems with undercuts. With the use of one of such attachment systems, an undercut is formed in the vicinity of a bore bottom with a special tool. An anchor rod, with an expansion sleeve mounted thereon, is inserted in the bore, in which the undercut has been formed, and the expansion tabs of the expansion sleeve expand radially upon displacement of the sleeve over a head portion of the anchor rod, which widens in the setting direction. The expansion tabs which have their ends engaged in the undercut, form a formlocking connection with the structural component.
With another type of an attachment system with an undercut, a need in a special tool for forming the undercut is eliminated, as the undercut is formed automatically during the setting process, resulting in formation of a formlocking attachment at the end of the setting process. The undercut is formed by providing cutters at the free ends of the expansion tabs and which, upon rotation of the expansion sleeve, which is simultaneously driven over the head portion of the anchor rod with axial blows, mill the undercut in the bore, with the expansion tabs engaging in the so-formed undercut at the end of the setting process, forming a formlocking connection with the structural component. In addition to the attachment systems with an undercut self-cutting dowel with a rotatable sleeve, also known are attachment systems with which an undercut is formed without the rotation of the expansion sleeve, only by chiseling the cylindrical bore wall during the setting process.
The attachment or fastening system can be formed of an anchor rod with a head portion widening in the setting direction, and an expansion sleeve displaceable along the anchor rod. Another attachment system includes a body having a through-bore and an inner thread formed in the rear portion of the through-bore, and an outer cone which is held in the through-bore with its smallest diameter portion.
For formlocking anchoring of such "outcone-dowel", the body is driven over the outer cone, which is supported against the bottom of a bore formed in a structural component, by axial blows. The radially expanding expansion tabs chisel an undercut in the bore wall. Whereas with the attachment systems with an undercut which include an anchor rod, in case of a dynamic load or in case of a torn concrete, a certain secondary expansion takes place, the "outconedowel" does not provide for a secondary expansion when a tension load is applied to the inner thread. Without a secondary expansion, a formlocking anchoring system can fail even upon application of a relatively small load in case of a dynamic loading or in case of a torn concrete.
Accordingly, an object of the present invention is to provide an outcone-dowel anchoring system with an undercut capable of withstanding high loads even in case of dynamic loading and/or in case of a tom concrete.